Dithiophosphate insecticides



2,884,354 Patented Apr. 28, 1959 2,884,354 DITHIOPHOSPHATE INSECTICIDES Domld L. Wilmington, Del., aaslgnor to Her- Chrlstman, cnles Powder Company, Wilmington, Del, a corporation of Delaware No Drawing. Application August 30, 1955 Serial No. 531,611

Claims. (Cl. 167-22) This invention relates to new and useful organic dithiophosphate compounds and to pesticidal compositions containing the same.

The novel organic dithiophosphate compounds of this invention have the general formula s entai -(0R),

s JJHrSl R)s in which each R represents a lower alkyl radical.

These organic dithiophosphate compounds have pesticidal properties and distinguish themselves in being highly toxic at low concentrations toward certain pests.

The organic dithiophosphate compounds of this invention are made by reacting bis(chloromethyl)sulfide (1,3- dichlorothiapropane) with the desired diester of dithiophosphoric acid, the latter being the product of reaction of an alcohol or a mixture of alcohols of the formula ROH in which R is an alkyl radical of 1-4 carbon atoms and s,. The diester of dithiophosphoric acid may be reacted directly with the bis(chloromethyl)sulfide, but it is more satisfactorily reacted in the form of its salt or in the presence of materials which sequester the hydrogen chloride set free in the reaction.

The methods of making the products of this invention and methods of using the products as pesticides are more particularly described in the following examples in which all parts and percentages are by weight. are degrees centigrade.

Example] Fifteen parts of pyridine was added to 41 parts of 0,0-diethyl dithiophosphoric acid in about 80 parts of lyzed: S, 37.0%; P, 15.1%; C1, 0.5% (calcd. for designated ester: S, 37.2%; P, 14.4%, Cl, 0.0%).

An emulsifiable concentrate of the residue was made by mixing 1 gram of the residue with 1 ml. benzene and 1 ml. sorbitan monolaurate polyoxyalkylene derivative (Tween This concentrate was then diluted with water to form dispersions of the residue in water varying in concentration from 1.0% to 0.025%. The dispersions were then tested for their toxicity to caged insects and to mites not only by spraying the insects but by spraying the plants alone as well for the purpose of determining Temperatures residual toxicity. Standard test methods were used for obtaining the toxicity results.

When a aphids were sprayed with a 0.1% emulsion of the co position of this example and placed on pea seedlings sprayed simultaneously with the same emulsion,

I there resulted 100% mortality in 48 hours.

Activity tests were also run by spraying lima bean seedlingsinfested with two-spotted mites to run oif with 0.1% aqueous emulsion. There resultedl00% mortality to the mites after 5 days.

A 0.1% emulsion gave a 100% kill of flies and a 70% kill of Mexican bean beetles.

Residual activity tests were also run by spraying lima bean seedlings to run off with 0.1% aqueous emulsion and, after drying, infesting with two-spotted mites after varying intervals of time. There resulted 100% mortality to the mites after 36 days, the counts being taken 5 days after the infestation date.

Example 2 A solution was prepared by dissolving 13.1 parts of bis(chloromethyl) sulfide, 0.2 part of hydroquinone, 1.5 parts of zinc chloride and 31.6 parts of 0,0-dimethyl dithiophosphoric acid in about 80 parts of benzene. A slight warming to 35 was noted, but heating to refluxing was continued for 2 hours with stirring. The reaction mixture was cooled and washed successively with brine, 1 molar sodium hydroxide, and water and then dried over magnesium sulfate. Removal of the solvent under reduced pressure and topping to 60 (0.4 mm.) yielded a light yellow oil (n 1.6084) weighing 27.8 parts. This oil which was thiapropane-l,3-dithiol S,S-bis(dimethyl phosphorodithioate) analyzed as follows: P, 15.7% (calcd. for the designated ester: P, 16.6%).

Tests on emulsions prepared as in Example 1 showed that a 0.1% emulsion of the composition of this example produced a kill of pea aphids when sprayed on pea plants infested with pea aphids.

Example 3 Thiapropane-l,3-dithiol S,Sbis(diisopropyl phosphorodithioate) was prepared by the same method used for the preparation of Example 2. It was a pale yellow oil, u 1.5580, analyzing 12.2% P, compared to a calculated value of 12.7% P.

Example 4 In the manner described in Example 1, thiapropanel,3dithiol S,S-bis(dibutyl.phosphorodithioate) was prepared and while found to be toxic to insects, exhibited somewhat less toxicity than the product of Example 3.

The organic dithiophosphate compounds of the formula GHa-Blii-(OR);

lilHs-Si(OR)r are those in which each R in the Y s Bl (OR)s group is the same or a dificrent lower alkyl radical such as methyl, ethyl, propyl or butyl. The preferred compounds are those containing iower alkyl radicals having l-4 carbon atoms. The compounds which are especially efiective as pesticides are those in which the R group is ethyl.

In producing the compounds of this invention, the reaction between the bis(chloromethyl)sulfide and the ester of dithiophosphoric acid or its salt is carried out by heating the two reactants at a temperature at which reaction takes place but below the decomposition temperature in the range of to 200' 0., preferably in the range of 30' to 110' C. In order to get complete reaction, it is preferable to use an excess over the theoretical amount of the ester of the dithiophosphoric acid. When the reaction is complete, the excess ester of the dithiophosphoric acid is readily removed by washing with water containing sutlicient alkali to produce the water-soluble salt.

The reaction is preferably carried out in non-aqueous media in which an organic solvent is used as a diluent to aid in control of the reaction. Suitable-solvents include benzene, toluene, xylene, cyclohexane, hexane, acetone, anhydrous alcohol solvents and dioxane. It is preferable to use acetone or aromatic hydrocarbon solvents when using an amine salt of the dithiophosphoric acid ester or when using an amine or ammonia as a sequestering reagent. After the reaction is complete, the solvent is readily removed bydistillation.

When the diester of dithiophosphoric acid is used in the form of the acid in the reaction with the bis(chloromethyl)sulfide hydrogen chloride which is liberated is preferably sequestered by adding a material to combine with the hydrogen chloride as formed. It is convenient to use pyridine for this purpose. However, in its place other tertiary organic amines may be used, and they may be added in equivalent amount at the beginning of the reaction or gradually during the course of the reaction. Likewise, the amine can be reacted with the diester of the dithiophosphoric acid prior to carrying out the reaction with the bis(chloromethyl)sulfide as in Example 1. Amines which can be used include pyridine, tertiary alkylamines such as ttimethylamine, tributylamine, triamylamine, dimethylanalinc, and the like. Inorganic bases may also be used. These include ammonia, alkali metal hydroxides, carbonates and bicarbonates, and alkaline earth metal hydroxides and carbonates.

As in the case of organic bases, the inorganic bases may also be used first to form a salt of the ester of the dithiophosphoric acid. When the salt of the ester of dithiophosphoric acid is used as the reactant, it is preferable to use a salt which is soluble in the organic solvent used for the reaction. The organic salts of amines are particularly satisfactory because of the good solubility of these salts in the nonreactive aromatic hydrocarbon solvents. When the free acid is reacted with the bis(chloromethyl)sulfide, the alkaline material is preferably added gradually as needed but it can be added all at once if desired. Ammonia is suitably added gradually as a gas, the solids are suitably added in finely divided form.

The dithiophosphoric acid ester is produced by reacting the lower aliphatic alcohol, which is to form a part of the ester, with P 5 preferably in a nonreactive solvent such as benzene, toluene, xylene, and removing the H 8 which is liberated. The reaction is carried out at any temperature in the range of 50 to 120 C., selecting the lowest practical temperature without decomposition. If different radicals are desired for the various R radicals, a mixture of alcohols may be used in the production of the dithiophosphoric acid ester. Likewise, dithiophosphoric acid esters produced from different alcohols can be mixed for use in the reaction with the bis(chloromethyl)sulfide. The esters of dithiophosphoric acid used in preparation of the compounds of this invention are thus made from individual alcohols or mixtures of a1- cohols having l-4 carbon atoms. Included among such alcohols are methanol, ethanol, propanol-l, and propanol-2.

The methods by which the products of this invention are isolated will vary slightly with the reactants used and the product produced. In some instances the chloride salt split out in the reaction separates and can be filtered off. In other instances the chloride salt is best removed by washing with water. The excess salt of the ester of dithiophosphoric acid is also removed by the water wash.

The benzene or other solvent is then removed by distillation leaving an insecticidally active residue. Further purification by selective solvent extraction or by adsorptive agents such as activated carbon, or clays, can precede the removal of the solvent.

' agents. However, the product is generally satisfactory for use as a pesticide without further purification.

The compounds of this invention are used as the sole toxic agent in pesticidal formulations or in admixture with other toxicants for modification of the properties of the individual toxicants. They may be used, for example, in admixture with toxaphene, DDT, Thanite, chlordane, rotenone, pyrethrum and the like in many of the formulations suggested below.

The compounds of this invention are made into pesticidal compositions for use against insects and mites by dilution with an insecticidal adjuvant as a carrier therefor, by dispersing in an organic solvent, or in water, or by diluting with a solid insecticidal adjuvant as a carrier. Dispersions containing a surface-active dispersing agent have the advantage of spreading the toxic substance more efiectively over the plant surface. Dispersions in organic solvents include dispersions or solutions in alcohols, pine oil, hydrocarbon solvents, ditluorodichlorornethane, and similar organic solvents. The compounds of this invention are also used in Aerosol formulations in which difluorodichloromethane and similar aerosol propellants form the propellant vehicle.

Aqueous dispersions are made up from the compounds of this invention, a surface-active dispersing agent and water as the essential ingredients. .The amount of the compounds of this invention in the aqueous dispersions when diluted for spraying of plants will be in the'range of about 10% to about 0.001% of the aqueous dispersion.

The aqueous dispersion will ordinarily be made up from a concentrate, and the concentrate will be dispersed in water to the proper concentration for application to the plants to be treated in the field. The concentrate is composed essentially of the compound of this invention and a surface-active dispersing agent. The concentrate may also contain suflicient amounts of organic solvents to aid in effective dispersion. The amount of surface-active dispersing agent used is usually at least 5% of the amount of toxic compound in the concentrate.

Suitable surface-active dispersing agents for use in the compositions of this invention are those disclosed in Chemistry of Insecticides, Fungicides, and Herbicides (Donald E. H. Frear, second edition (1948), pages 280-287) for use with known insecticides and include neutral soaps of resin, alginic and fatty acids and alkali metals or alkylamines or ammonia, saponins, gelatins, milk, soluble casein, flour and soluble proteins thereof, sulfite lye, lignin pitch, sulfite liquor, long-chain fatty alcohols having 12-18 carbon atoms and alkali metal salts of the sulfates thereof, salts of sulfated fatty acids, salts of sulfonic acids, esters of long-chain fatty acid! and polyhydric alcohols in which alcohol groups are free, clays such as fullers earth, China clay, kaolin, attapulgi-te, and bentonite and related hydrated aluminum silicates having the property of forming a colloidal gel. Among the other surface-active dispersing agents which are useful in the compositions of this invention are the omega-substituted polyethylene glycols of relatively long-chain length, particularly those in which the omega substituent is aryl, alkyl, or acyl. Compositions of the toxic material and surface-active dispersing agent will, in some instances, have more-than one surface'active dispersing agent for a particular type of utility, or in addition to a surface-active dispersing agent, hydrocarbons such as kerosene and mineral oil will also be added as improvers. Thus, the toxic material may contain a clay as the sole adjuvant or clay and hydrocarbon, or clay and another surface-active dispersing agent to augment the dispersing action of the clay. Likewise, the toxic material mayhave water admixed therewith along with the surface-active dispersing agent, sufiicient generally being used to form an emulsion. All of these compositions of toxic material and surface-active dispersing agent may contain, in addition, synergists and/ or adhesive or sticking agents.

What I claim and desire to protect by Letters Patent 1s:

1. As a new composition of matter a compound of the formula JHzSl -(OR)a in which each R represents a lower alkyl radical.

2. As a new composition of matter a compound of the formula in which R and R' represent different lower alkyl radicals.

3. As a new composition of matter a compound of the formula S OHPSl -(O CH):

4. As a new composition of matter a compound of the formula 5. As a new composition of matter a compound of 10 the formula References Cited in the file of this patent UNITED STATES PATENTS 30 2,494,126 Hoegberg Ian. 10, 1950 2,494,283 Cassaday et al. Ian. 10, 1950 2,571,989 Schrader Oct. 16, 1951 FOREIGN PATENTS 85 515,666 Canada Aug. 16, 1955 

1. AS A NEW COMPOSITION OF MATTER A COMPOUND OF THE FORMULA
 6. A PESTICIDAL COMPOSITION COMPRISING A COMPOUND OF CLAIM 1 AND AN INSECTICIDAL ADJUVANT. 